Do keyboards even have a language, or just different stickers on the keys ?

I could maybe take advantage of the fact that I'm using two different models. I'm open to a low level solution (something like listening to keyboard inputs and switch language accordingly, if you can find the origin on the USB bus of a keystroke, but it would be a programming question for StackOverflow I guess).

Keyboards are all electrically the same, just the printing is different. What a key produces is determined by the software on the machine and is normally the same for all attached keyboards. But I think I have heard that Keyremap4Macbook can distinguish between hardware keyboards, so you may want to check that app.
– Tom GeweckeMay 15 '14 at 17:07